CHAPTEK X 



PHYSIOLOGY OF VASCULAR MUSCLE AND NERVES 



SUMMARY. 1. Discovery of vasomotor nerves. 2. Vascular tone and its 

 rhythmic and a-rhythmical variations, as depending essentially upon the automatic 

 and reflex excitability of the smooth muscle cells. 3. Theory of vaso-constrictor 

 nerves. 4. Theory of vaso-dilator nerves. 5. Vascular reflexes. 6. Bulbar vaso- 

 constrictor centre. 7. Spinal and cerebral centres for vaso-constrictor nerves. 

 8. Centres for vaso-dilator nerves. Bibliography. 



THE preceding chapter on the physiology of cardiac muscle and 

 the cardiac nerves will facilitate our investigation of the physiology 

 of the muscle cells and nerves with which the walls of the blood- 

 vessels are provided. As we shall see, there is an exact analogy 

 between the physiological phenomena in both cases. 



I. After Haller, Spallanzani, Magendie, and Poiseuille had 

 demonstrated the possibility of the circulation of the blood, in 

 virtue simply of the heart's activity as a force-pump, and the 

 physical elasticity of the blood-vessels, the older theories as to the 

 importance to the circulation of the muscle cells and vascular 

 nerve fibre were disregarded and almost forgotten. At the 

 commencement of the last century, however, certain normal and 

 pathological phenomena, which directly contradicted the purely 

 mechanical theory, again attracted the attention of physicians 

 and physiologists. Among these, are : abnormal conditions of 

 temperature and nutrition in paralysed limbs, circulatory changes 

 (blushes and pallor) due to emotional states or to neuralgia, 

 hyperaemia, and congestion at the seat of inflammation, pneumonia 

 after section of the vagi, panophthalmia on dividing the trigeminal, 

 failure of erection of penis, when the spinal nerves have been 

 divided, and so on. 



The precursors of the physiology of the active movements of 

 the vessels included E. H. Weber (1831), Henle (1840), Stilling 

 (1840), Valentin and Schiff (1844), who adumbrated not a few of 

 the facts and theories which subsequently received experimental 

 confirmation. 



In 1851 Claude Bernard discovered and described the 

 phenomena that occur in the vessels of the rabbit's ear, on 



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